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<head>
    <meta charset="UTF-8">
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    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
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<body>
    
</body>
<script>
    /**
     * unshift(被添加元素) push(被添加元素)
     */
    var currentDay="星期4";
    var dayList=[currentDay];
    var str= dayList.unshift("星期二");
    var str1=dayList.unshift("星期三");
    console.log(str);
    console.log(str1);
    var arr1=["hello","world"];
    var arr2=["hello","javascript"];
    var arr3=["arr3"];
    /**
     * arr.concat(arr1,arr2)
     * 会将arr arr1 arr2 合并 得到一个新数组 但不会对arr产生影响
     */
    var arr4=arr1.concat(arr2,arr3);
    console.log(arr4);

</script>
</html>